feat(tags): Add tag archive route and admin interface integration

Implement Phase 3 of v1.3.0 tags feature per microformats-tags-design.md:

Routes (starpunk/routes/public.py):
- Add /tag/<tag> archive route with normalization and 404 handling
- Pre-load tags in index route for all notes
- Pre-load tags in note route for individual notes

Admin (starpunk/routes/admin.py):
- Parse comma-separated tag input in create route
- Parse tag input in update route
- Pre-load tags when displaying edit form
- Empty tag field removes all tags

Templates:
- Add tag input field to templates/admin/edit.html
- Add tag input field to templates/admin/new.html
- Use Jinja2 map filter to display existing tags

Implementation details:
- Tag URL parameter normalized to lowercase before lookup
- Tags pre-loaded using object.__setattr__ pattern (like media)
- parse_tag_input() handles trim, dedupe, normalization
- All existing tests pass (micropub categories, admin routes)

Per architect design:
- No pagination on tag archives (acceptable for v1.3.0)
- No autocomplete in admin (out of scope)
- Follows existing media loading patterns

Generated with Claude Code

Co-Authored-By: Claude <noreply@anthropic.com>

starpunk/routes/admin.py

@@ -78,6 +78,7 @@ def create_note_submit():
         custom_slug: Optional custom slug (v1.2.0 Phase 1)
         media_files: Multiple file upload (v1.2.0 Phase 3)
         captions[]: Captions for each media file (v1.2.0 Phase 3)
+        tags: Comma-separated tag list (v1.3.0 Phase 3)
 
     Returns:
         Redirect to dashboard on success, back to form on error
@@ -85,21 +86,27 @@ def create_note_submit():
     Decorator: @require_auth
     """
     from starpunk.media import save_media, attach_media_to_note
+    from starpunk.tags import parse_tag_input
 
     content = request.form.get("content", "").strip()
     published = "published" in request.form
     custom_slug = request.form.get("custom_slug", "").strip()
+    tags_input = request.form.get("tags", "")
 
     if not content:
         flash("Content cannot be empty", "error")
         return redirect(url_for("admin.new_note_form"))
 
+    # Parse tags (v1.3.0 Phase 3)
+    tags = parse_tag_input(tags_input)
+
     try:
         # Create note first (per Q4)
         note = create_note(
             content,
             published=published,
-            custom_slug=custom_slug if custom_slug else None
+            custom_slug=custom_slug if custom_slug else None,
+            tags=tags if tags else None
         )
 
         # Handle media uploads (v1.2.0 Phase 3)
@@ -167,12 +174,18 @@ def edit_note_form(note_id: int):
     Decorator: @require_auth
     Template: templates/admin/edit.html
     """
+    from starpunk.tags import get_note_tags
+
     note = get_note(id=note_id)
 
     if not note:
         flash("Note not found", "error")
         return redirect(url_for("admin.dashboard")), 404
 
+    # Pre-load tags for the edit form (v1.3.0 Phase 3)
+    tags = get_note_tags(note.id)
+    object.__setattr__(note, '_cached_tags', tags)
+
     return render_template("admin/edit.html", note=note)
 
 
@@ -191,12 +204,15 @@ def update_note_submit(note_id: int):
     Form data:
         content: Updated markdown content (required)
         published: Checkbox for published status (optional)
+        tags: Comma-separated tag list (v1.3.0 Phase 3)
 
     Returns:
         Redirect to dashboard on success, back to form on error
 
     Decorator: @require_auth
     """
+    from starpunk.tags import parse_tag_input
+
     # Check if note exists first
     existing_note = get_note(id=note_id, load_content=False)
     if not existing_note:
@@ -205,13 +221,22 @@ def update_note_submit(note_id: int):
 
     content = request.form.get("content", "").strip()
     published = "published" in request.form
+    tags_input = request.form.get("tags", "")
 
     if not content:
         flash("Content cannot be empty", "error")
         return redirect(url_for("admin.edit_note_form", note_id=note_id))
 
+    # Parse tags (v1.3.0 Phase 3)
+    tags = parse_tag_input(tags_input)
+
     try:
-        note = update_note(id=note_id, content=content, published=published)
+        note = update_note(
+            id=note_id,
+            content=content,
+            published=published,
+            tags=tags if tags else None
+        )
         flash(f"Note updated: {note.slug}", "success")
         return redirect(url_for("admin.dashboard"))
     except ValueError as e: